Around 12 police officers were among the injured as police skirmished with protesting groups in an effort to keep them away from the convention center where 15 EU leaders were meeting.

Plumes of smoke rose over the fashionable Kungsports Avenyn as masked anarchists methodically vandalised shop windows, piled tables and chairs from sidewalk cafes into makeshift barricades and set them ablaze. Some stores were looted.

Protesters hurled paving-stones and firecrackers at police, who responded with baton charges. Some mounted police were dragged from their horses.

At times the protesters were less than one kilometre from the site of the summit, but other than forcing the cancellation of a dinner in a posh Gothenburg site, the summit has been largely unaffected by the violence and the protests.

As many as 12,000 protesters have staged demonstrations throughout the streets in the port city, while as many as 2,000 extra police were brought in for the summit and for the visit of U.S. President George W. Bush.

Swedish Justice Minister Thomas Bodstrom said at least two of the people who had been shot were anti-capitalist protesters.

Bodstrom denied police had lost control but said the violence by hundreds of anarchists was the most difficult challenge Sweden's security forces had ever faced.

"Many of the rioters came from other countries with the intention of disrupting the summit," he said.

Barricaded in a heavily guarded conference center, the 15 EU leaders condemned the anti-capitalist riots, which have dogged international gatherings since the 1999 World Trade Organisation conference in Seattle.

Five summit delegations were forced to move out of a central hotel because police said they could not guarantee their safety.

The mayhem overshadowed the day's EU business, which centred on the bloc's ambitious plans to admit up to 12 ex-communist and Mediterranean countries over the next few years.

In a park near Goteborg University, rioters smashed the windows of police vans and hurled rocks, cans and other debris at helmeted police, some mounted on horses.

The clashes were believed to be sparked by a small minority of the estimated 25,000 protesters who converged on the city for the summit.